DE102017128488A1 - A method and cell population sensor for determining a value indicative of the permittivity of a cell population - Google Patents

Abstract

A method for determining a value indicative of the permittivity of a cell population in the context of impedance spectroscopy comprises the steps of: generating an excitation current oscillating at an excitation frequency through the cell population; Measuring a voltage in the cell population between a first measuring electrode (12) and a second measuring electrode (14); Sampling the excitation current, generating first samples of the excitation current; Sensing the voltage between the first sensing electrode (12) and the second sensing electrode (14) to generate second voltage samples between the first sensing electrode and the second sensing electrode; and determining the value indicative of the permittivity of the cell population based on the first samples and the second samples.

Description

The present invention is in the field of impedance spectroscopy of cell populations. In particular, the present invention relates to determining the permittivity of a cell population or determining a value indicative of the permittivity of a cell population. More particularly, the present invention relates to a method and a cell population sensor for determining a value indicative of the permittivity of a cell population.

Electrical impedance spectroscopy techniques are used as a measurement method for nondestructive in situ and in vivo determination of frequency dependent passive electrical properties of biological materials. Such a biological material may be, for example, a substance of a liquid and biological cells received therein, referred to collectively herein as a cell population. The above-mentioned frequency-dependent passive-electrical properties of the cell population can provide, inter alia, information about the number of living cells and / or size of the cells and / or homogeneity of the cells. Previous sensors and impedance spectroscopy methods are not always completely satisfactory in terms of the accuracy of the measurement results. Also, the quality of the measurement results can vary widely over a wide frequency range.

Accordingly, it would be desirable to provide a method and a cell population sensor for determining a value indicative of the permittivity of a cell population having high measurement accuracy and enabling reliable measurements over a wide frequency range.

Exemplary embodiments of the invention include a method for determining a value indicative of the permittivity of a cell population in the context of impedance spectroscopy, comprising the steps of: generating an excitation current oscillating at an excitation frequency through the cell population; Measuring a voltage in the cell population between a first measuring electrode and a second measuring electrode; Sampling the excitation current, generating first samples of the excitation current; Sensing the voltage between the first sensing electrode and the second sensing electrode, generating second voltage samples between the first sensing electrode and the second sensing electrode; and determining the value indicative of the permittivity of the cell population based on the first samples and the second samples.

Exemplary embodiments of the invention enable a highly accurate determination of a value indicative of the permittivity of a cell population over a wide frequency range. Scanning the excitation current and sensing the voltage between the first sensing electrode and the second sensing electrode enable the first and second sensing samples to be generated at precisely predetermined times. These time discretized samples may be analyzed and correlated after sampling without the need for downstream signal processing to be real-time capable. A relatively large database clearly defined by sampling in the time dimension can be used to determine with high precision the value indicative of the permittivity of the cell population. Compared to previous approaches based on detecting characteristic cell population characteristics through complicated common analog signal processing of the excitation current and the voltage between the sensing electrodes, exemplary embodiments of the invention make it possible to minimize the parasitics after sampling since the signal processing of the discretized samples is very robust can be trained. The interference between the measurement of exciting current and voltage between the measuring electrodes as well as the sensing of excitation current and voltage between the measuring electrodes can be kept very low compared to the disturbances along the analog signal processing chains of the earlier approaches. Fault-prone additions, multiplications and integrations of analog signals for excitation current and voltage between the measuring electrodes, as used in earlier approaches, can be eliminated. Furthermore, the sampling of the excitation current and the voltage between the first measuring electrode and the second measuring electrodes can be tuned to the exciter frequency, whereby a high accuracy of the sampling at the relevant frequencies and a spectral limitation of the disturbing influences can be made possible.

The generation of the excitation current oscillating with the excitation frequency, the measurement of the voltage between the measuring electrodes, the scanning of the excitation current and the scanning of the voltage between the measuring electrodes take place simultaneously. In other words, the voltage between the first measuring electrode and the second measuring electrode is measured and sampled, while the excitation current oscillating with the excitation frequency is applied to the cell population. Accordingly, the electrical behavior of the cell population is measured upon application of the excitation current oscillating with the exciter frequency.

The sampling of the excitation current and the sampling of the voltage between the first measuring electrode and the second measuring electrode may include Scanning of derived values of excitation current and voltage between the measuring electrodes. For example, a first signal can be generated for the excitation current, which images the exciter current. This first signal may be, for example, a voltage signal. The first signal can then be sampled directly or after amplification. Also, such signal processing falls within the meaning of the present document under the concepts of scanning the excitation current and generating first samples for the excitation current. It is also possible that the voltage between the first measuring electrode and the second measuring electrode is tapped in the form of a second signal. This second signal can also be sampled either directly or amplified. As with the sampling of the exciting current, such preprocessing of the second signal also falls within the concepts of sampling the voltage between the first measuring electrode and the second measuring electrode and generating second sampling values in the sense of the present document.

The cell population is an accumulation of biological cells. In particular, the cell population contains a significant proportion of living cells. The cells may be present in a carrier material. For example, the cells may be accommodated in the form of a suspension in a carrier liquid. The term cell population may refer to the accumulation of biological cells including the carrier material.

In another embodiment, sensing the excitation current and sensing the voltage between the first sensing electrode and the second sensing electrode each include converting an analog signal to a digital signal. In this way, discrete-time and discrete-value samples are present both for the exciter current and for the voltage between the measuring electrodes. These can be processed completely digitally and detached from the real time, which results in great flexibility, accuracy and consistency in the further processing for the analysis of exciter current and voltage between the measuring electrodes. Highly accurate results over a wide frequency range can be achieved.

According to a further embodiment, the method further comprises the following steps: setting a first sampling rate for sampling the excitation current and setting a second sampling rate for sampling the voltage between the first measuring electrode and the second measuring electrode. In particular, the setting of the first sampling rate and / or the setting of the second sampling rate can be carried out on the basis of the exciter frequency of the exciter current. The first sampling rate and the second sampling rate may be the same or different. The setting of the first sampling rate and the setting of the second sampling rate make it possible to adapt the determination of the value indicating the permittivity of the cell population to the boundary conditions of a present measurement process, in particular to the exciter frequency of the exciter current for the present measurement process. In this way, it is possible to use optimized sampling rates for each measurement process, in particular to set a sampling rate optimized in terms of accuracy and / or signal processing complexity. The first sampling rate and the second sampling rate are used for sampling the exciting current or for sampling the voltage between the first measuring electrode and the second measuring electrode. As a result, the first sampling rate and the second sampling rate are set prior to sampling the exciting current and the voltage between the measuring electrodes.

According to a further embodiment, the first sampling rate and the second sampling rate are set to at least 4 times the excitation frequency of the excitation current. By using at least 4 times the excitation frequency of the excitation current for sensing excitation current and voltage between the measuring electrodes, it is ensured that excitation current and voltage between the measuring electrodes are sampled very accurately and that no signal information around the excitation frequency is lost. The sampling theorem is overreached with reassuring distance. In particular, the first sampling rate and the second sampling rate may be set at substantially 4 times the exciting frequency of the exciting current or even exactly 4 times the exciting frequency of the exciting current.

According to another embodiment, the excitation frequency of the excitation current is between 50 kHz and 20 MHz. With an excitation current in this frequency range, particularly relevant values indicative of the permittivity of the cell population can be ascertained, which in particular give a good indication of the quantities and / or the size and / or homogeneity of the living cells of the biomass. The said frequency range lies in the so-called β-dispersion region of many cell populations, which will be discussed in detail below.

According to a further embodiment, the scanning of the exciter current and the sampling of the voltage between the first measuring electrode and the second measuring electrode is synchronized. In this way, a high-precision correspondence between the sampled excitation current and the sampled voltage between the measuring electrodes can be achieved, whereby the phase shift between excitation current and voltage between the measuring electrodes can be determined with high accuracy, which in turn highly accurate determination of the value indicative of the permittivity of the cell population. A synchronized scanning of the excitation current and the voltage between the measuring electrodes is understood herein to mean a simultaneous sampling within the scope of manufacturing tolerances or a sampling with an offset defined in the context of manufacturing tolerances. The defined offset can subsequently be taken into account in the further processing of the first and second samples.

According to another embodiment, the variation of the sampling instant, i. the jitter for sampling the exciting current and sensing the voltage between the first measuring electrode and the second measuring electrode is less than 500 fs. Such a design helps that the excitation current and the voltage between the measuring electrodes can be repeatedly sampled synchronously with high accuracy.

According to a further embodiment, the method comprises writing the first samples and the second samples into a data memory. The provision of a data memory for directly recording the first samples and the second samples produces a well-defined location at which the information about the excitation current and the voltage between the measuring electrodes is provided and from which the further processing without real-time requirements and over a series of Samples. The data memory is a safe depot for the information obtained from excitation current and voltage between the measuring electrodes. In another embodiment, the data store is capable of receiving data at a data acquisition rate of at least 1 Gbit / s. In this way, a complete recording of the samples can be ensured even at high sampling rate and high resolution.

According to another embodiment, the step of determining the value indicative of the permittivity of the cell population includes applying a complex Fourier transform to the first samples and the second samples. In particular, a complex discrete Fourier transformation can be used here. The samples of the exciting current and the samples of the voltage between the first measuring electrode and the second measuring electrode may be considered as respective real parts of a complex current or voltage signal. By means of complex Fourier transformation, which takes into account the first and second samples together, the complex impedance between excitation current and voltage between the measuring electrodes can be determined. In particular, it is possible to determine the complex impedance at the excitation frequency, which can be the basis for the value indicating the permittivity of the cell population.

According to a further embodiment, the step of determining the value indicative of the permittivity of the cell population comprises at least one of the following steps: determining the amplitude of the oscillating excitation current; Determining the spectral component of the voltage having the excitation frequency; and determining the phase shift between exciting current and said spectral component of the voltage. In particular, the step of determining the value indicative of the permittivity of the cell population may comprise exactly one or each subset or all of the said steps.

According to a further embodiment, the step of determining the value indicative of the permittivity of the cell population comprises the step of: determining the value indicative of the permittivity of the cell population based on one or more of the amplitude of the oscillating excitation current, the amplitude of that spectral component of the voltage, which has the excitation frequency, and the phase shift between the exciting current and the said spectral component of the voltage. In particular, for determining the value indicative of the permittivity of the cell population, the amplitude of the oscillating excitation current as well as the amplitude of said spectral component of the voltage as well as the phase shift between exciting current and said spectral component of the voltage can be used. In particular, the capacity of the cell population between the measuring electrodes can be calculated on the basis of the amplitude of the oscillating excitation current, the amplitude of said spectral component of the voltage and the phase shift between exciting current and said spectral component of the voltage. The capacity may be the value indicative of the permittivity of the cell population. It is furthermore possible for the permittivity to be determined from the capacitance or directly on the basis of the amplitude of the oscillating exciter current, the amplitude of the said spectral component of the voltage and the phase shift between the excitation current and the said spectral component of the voltage.

According to a further embodiment, the value indicative of the permittivity of the cell population is a capacitance value, in particular a capacitance value, which characterizes the capacity of the cell population between the measuring electrodes, or a permittivity value, in particular the permittivity of the cell population itself.

In another embodiment, the step of sampling the excitation current amplifying a first signal representative of the exciting current before generating the first samples based on the amplified first signal. In this way, the demands on the accuracy of generating the first samples can be kept comparatively low. The amplification of the first signal makes it possible to represent small variations of the excitation current on a larger scale. It may be advantageous for the overall complexity and / or accuracy of the overall system to invest in a highly linear amplification of the first signal and to make lower demands on the sampling of the amplified first signal.

In another embodiment, the step of sensing the voltage between the first sensing electrode and the second sensing electrode includes amplifying a second signal representative of the voltage between the first sensing electrode and the second sensing electrode before generating the second sensing values based on the amplified second signal. The above considerations regarding overall complexity and / or overall accuracy apply mutatis mutandis to generating the second samples from the voltage measured between the measuring electrodes.

According to a further embodiment, the method comprises the step of generating a first signal representing the exciting current via a measuring element. The measuring element can be a measuring resistor. In particular, the measuring resistor may have a resistance of 30 Ω to 50 Ω. The first samples can be generated directly from the first signal obtained via the measuring element. However, it is also possible for the first signal to be amplified first before the first samples are generated.

According to a further embodiment, generating the excitation current oscillating with the excitation frequency through the cell population includes galvanic decoupling between an AC current source emitting the excitation current, e.g. an oscillator, and the cell population. The capacitive artifacts in the cell population caused by the current source can be kept low, so that the galvanic decoupling furthermore helps the high measuring accuracy. It is also possible to reduce external interfering couplings in the region of the electrodes via the galvanic decoupling. Galvanic decoupling may be via a transformer, optionally in combination with a capacitor, as described in detail below.

According to another embodiment, the method further comprises the steps of: determining a spectral power of the exciting current and the spectral component of the voltage having the exciting frequency; Determining the total power of exciting current and voltage between the first measuring electrode and the second measuring electrode; and determining a measure of the measurement accuracy of the value indicative of the permittivity of the cell population based on said spectral power and the total power. In particular, said measure may be the signal-to-noise ratio between said spectral power and the noise power. The noise power can be calculated as the difference between the total power and the mentioned spectral power. By comparing said spectral power and the total power, an estimate can be made of what proportion of the measured voltage between the measuring electrodes is due to the excitation current, i. which proportion of the measured voltage represents the behavior of the cell population to be investigated. The noise power may include both the excitation current induced responses of the cell population and the measuring apparatus at frequencies other than the excitation frequency as well as voltages generated elsewhere in the cell population. Accordingly, said measure is an indicator of what degree the spectral component of the voltage having the excitation frequency may be corrupted. The measure may be output to a user as additional information. However, it may also be processed such that the determination of the value indicative of the permittivity of the cell population is repeated either equal to or at a later time.

Exemplary embodiments of the invention further comprise a method for deriving at least one characteristic property of a cell population, comprising the following steps: performing the method several times to determine a value indicating the permittivity of a cell population according to one of the above-described embodiments, wherein performing the method several times using a plurality of different excitation frequencies and determining a plurality of cell population permittivity indicative values for the plurality of different excitation frequencies; and deriving the at least one characteristic of the cell population by relating the plurality of values indicative of the permittivity of the cell population. Herein, the relating may involve forming a difference between two values indicative of the permittivity of the cell population and / or determining the slope of a curve include determining the values indicative of the permittivity of the cell population, and / or determining a point of inflection of a curve set by the plurality of values indicative of the permittivity of the cell population, and / or determining further characteristic features of the plurality of values indicative of the permittivity of the cell population. It is possible to deduce the characteristic properties of the cell population via these characteristic properties of the amount of values obtained. By highly accurately determining the plurality of cell population permittivity indicative values over a relatively large frequency range, the characteristics of the cell population can also be determined with high accuracy.

According to a further embodiment, said method is for determining a value indicative of the permittivity of a cell population for between 2 and 50 different exciter frequencies. In particular, the method for determining a permittivity of a cell population indicative value for between 10 and 40 different excitation frequencies, more particularly for between 20 and 30 different exciter frequencies can be performed. It has been found that for the stated number of runs of the method and the corresponding number of values indicative of the permittivity of the cell population, in particular at between 10 and 40 different exciter frequencies or more particularly between 20 and 30 different exciter frequencies, a good compromise between The complexity of the method for deriving at least one characteristic property of the cell population and accuracy of the results regarding the at least one characteristic property of the cell population can be achieved. In particular, particularly meaningful curves of the value indicative of the permittivity of the cell population, in particular of the permittivity itself, can be generated for between 10 and 40 different exciter frequencies, or more particularly for between 20 and 30 different exciter frequencies. The stated number of values allows the generation of paths with respect to the excitation frequency with sufficient accuracy to determine characteristic properties such as slope and turning point with high accuracy.

According to a further embodiment, the different excitation frequencies come from a frequency range of 100 kHz to 10 MHz. The expression that the different excitation frequencies originate from said frequency range means that at least the said frequency range is covered by the different exciter frequencies. This in turn means that the lowest excitation frequency is 100 kHz or less and that the highest excitation frequency is 10 MHz or more. In other words, the lowest exciter frequency and the highest exciter frequency form an intermediate excitation frequency span, which includes at least the range between 100 kHz to 10 MHz. With the permittivity of the cell population indicative values for the excitation frequencies of 100 kHz to 10 MHz, one or more characteristic properties of a plurality of cell populations can be determined with high accuracy.

In a further embodiment, the different excitation frequencies come from a frequency range of 50 kHz to 20 MHz. It has been found that by the above-described scanning of the excitation current and the voltage between the first measuring electrode and the second measuring electrode, even for such a large excitation frequency range between 50 kHz and 20 MHz, highly accurate values indicative of the permittivity of the cell population can be determined. As a result, the derivation of the at least one characteristic property of the cell population can be further refined. Thus, the above-described method for determining a permittivity of a cell population indicative of an increase in the frequency range of impedance spectroscopy and thus a more comprehensive determination of one or more characteristics of the cell population, without having to resort to additional and more expensive procedures. It is also possible that the method can be applied to an extended range of cell populations.

According to another embodiment of the invention, each instance of performing the method of determining a value indicative of the permittivity of a cell population takes between 10 ms and 100 ms each time. In particular, each instance of repeated execution of the method lasts between 30 ms and 70 ms. Accordingly, it is possible to derive one or more characteristic features of a cell population in a very short period of time, on the order of a few seconds. Thus, the present method according to exemplary embodiments of the invention allows the user to have almost immediate and therefore extremely convenient determination of one or more characteristics of the cell population. The removal of samples of a cell population and the time-offset or spatially offset analysis of the samples can be omitted.

According to a further embodiment, deriving the at least one characteristic characteristic of the cell population includes establishing a progression of the values indicative of the permittivity of the cell population over the different exciter frequencies. In other words, there can be a curve through which the permittivity of the Cell population indicative values are placed opposite the exciter frequency. In this case, a so-called Cole-Cole fitting can be used. From the resulting curve or from the resulting course then characteristics such. B. Differences between end values, slopes and turning points can be determined. The values indicative of the permittivity of the cell population may directly be the determined values as described above or calibrated versions of the determined values.

According to a further embodiment, the at least one characteristic property of the cell population comprises at least one property of number of living cells, size of the cells and homogeneity of the cells.

Exemplary embodiments of the invention further include a cell population sensor for determining a value indicative of the permittivity of a cell population, comprising: an oscillator circuit; a first exciter electrode and a second exciter electrode, which are coupled to the oscillator circuit, wherein by means of the oscillator circuit via the first and the second excitation electrode an exciting current oscillating with an exciter frequency can be generated by the cell population; a first measuring electrode and a second measuring electrode for measuring a voltage in the cell population between the first and second measuring electrodes; a first sampling circuit coupled to the first excitation electrode and / or the second excitation electrode and providing in operation first samples of the oscillatory excitation current; a second sense circuit coupled to the first and second sense electrodes and in operation providing second samples of the voltage between the first and second sense electrodes; and data processing means coupled to the first sampling circuit and the second sampling circuit and configured to determine the value indicative of the permittivity of the cell population based on the first samples and the second samples. The additional features, modifications, and technical effects described above with respect to the method of determining a cell population permittivity indicative value are analogous to the cell population sensor.

The first and second sampling circuits operate simultaneously during operation, i. they generate the first samples for the exciting current and the second samples for the voltage between the first and second measuring electrodes in the same period. Furthermore, in operation, the first and second sampling circuits operate when the excitation current is present in the cell population, i. the first and the second sampling circuit operate in the same period as the oscillator circuit.

The term coupled is used herein to indicate that a signal or electrical quantity may be transmitted from one entity to another, i. that there is some kind of connection between the entities. However, other components, such as e.g. Amplifiers, transformers or other electrical components, be interposed.

The first sensing circuit may be coupled to either the first excitation electrode or the second excitation electrode. It can also be coupled to both exciter electrodes. In general, the first sensing circuit may be coupled in any suitable manner to one or both excitation electrodes such that measurement of the excitation current is possible.

According to a further embodiment, the first sampling circuit is a first analog-digital converter and the second sampling circuit is a second analog-digital converter.

According to a further embodiment, the first sampling circuit has a first settable sampling rate and the second sampling circuit has a second settable sampling rate. According to a further embodiment, the first adjustable sampling rate and the second adjustable sampling rate are adjustable to at least 4 times the exciter frequency of the exciter current. That is, the first sampling circuit and the second sampling circuit are capable of sampling the incoming signal at least 4 times the exciting frequency. In a further embodiment, the first adjustable sampling rate and the second adjustable sampling rate are substantially adjustable to 4 times or exactly 4 times the excitation frequency of the exciter current.

According to a further embodiment, the oscillator circuit is set up to set the excitation frequency in a frequency range from 100 kHz to 10 MHz. That is, the oscillator circuit is capable of adjusting the excitation frequency in a frequency range of 100 kHz to 10 MHz. This formulation does not exclude that the oscillator circuit can set the exciter frequency beyond the specified frequency range. Rather, the phrase means that the oscillator circuit is capable of adjusting the excitation frequency at least in the frequency range of 100 kHz to 10 MHz. In particular, the oscillator circuit can be set up to set the excitation frequency at least in a frequency range from 50 kHz to 20 MHz.

According to a further embodiment, the first sampling circuit and the second sampling circuit are synchronized with respect to their sampling times.

According to a further embodiment, the variation of the sampling time, ie the jitter, the first sampling circuit and the second sampling circuit is less than 500 fs. Such a design helps that the excitation current and the voltage between the measuring electrodes can be repeatedly sampled synchronously with high accuracy.

According to a further embodiment, the first sampling circuit and the second sampling circuit are coupled to the data processing device via a data memory, the data memory in particular having a data acquisition rate of at least 1 Gbit / s. The data acquisition rate of at least 1 Gbit / s describes a possible data acquisition rate of at least 1 Gbit / s. The data does not need to be picked up by the data store at this speed. Since the sampling frequency may depend on the excitation frequency, different data acquisition rates on the data memory may result in operation for different exciter frequencies.

According to a further embodiment, the data processing device is set up to determine the value indicative of the permittivity of the cell population by means of complex Fourier transformation from the first samples and the second samples.

According to a further embodiment, the data processing device is set up to determine at least one of the amplitude of the oscillating excitation current, the amplitude of the spectral component of the voltage having the excitation frequency, and the phase shift between the excitation current and the said spectral component of the voltage from the first samples and the second samples. In particular, the data processing device can be set up to determine exactly one or a subset or all of the named values.

According to a further embodiment, the data processing device is set up, the value indicative of the permittivity of the cell population based on one or more of the amplitude of the oscillating excitation current, the amplitude of that spectral component of the voltage having the excitation frequency, and the phase shift between the excitation current and the said Spectral component to determine the voltage. In particular, the data processing device can be set up to determine the value indicative of the permittivity of the cell population on the basis of the amplitude of the oscillating excitation current as well as the amplitude of said spectral component of the voltage and the phase shift between exciting current and said spectral component of the voltage.

According to a further embodiment, the value indicative of the permittivity of the cell population is a capacitance value or a permittivity value, in particular the permittivity of the cell population itself.

According to a further embodiment, the first sampling circuit is coupled to the first excitation electrode and / or the second excitation electrode via a first amplifier circuit, and the second sampling circuit is coupled to the first and the second measuring electrodes via a second amplifier circuit.

According to a further embodiment, a measuring element, in particular a measuring resistor, is coupled to the first exciter electrode or the second exciter electrode, and the first scanning circuit is arranged to provide the first samples for the oscillating exciter current on the basis of the voltage drop across the measuring element. For symmetry reasons, both excitation electrodes can each be coupled to a measuring element, in particular to a measuring resistor, even if the first sampling circuit is coupled to only one of the measuring elements.

According to a further embodiment, the oscillator circuit is coupled via a transformer to the first exciter electrode and the second exciter electrode.

According to another embodiment, the transformer has a parallel capacitance of 0.5 pF to 10 pF, in particular a parallel capacitance of 1 to 5 pF.

The parallel capacitance may be a discrete component, such as a capacitor arranged in parallel with the transformer. But it is also possible that the parallel capacitance is a parasitic capacitance of the transformer, wherein the transformer is designed so that the parallel capacitance is in the specified value range. The term parallel capacitance denotes a coupling capacitance between the primary side and the secondary side of the transformer. With a parallel capacitance, the influence of interfering coupling capacitances, such as may exist between the electrodes and the wall of a container for the cell population or between the electrodes and other existing sensors, can be minimized. Since, in the presence of the capacitance parallel to the transformer and other coupling capacitances, the smaller capacitance often determines, the influence of an undesired disturbing coupling capacitance on the size of the parallel capacitance can be reduced.

According to a further embodiment, the data processing device is set up to determine a spectral power of the exciter current and the spectral component of the voltage which has the excitation frequency and to determine the total power of excitation current and voltage between the first measuring electrode and the second measuring electrode. Furthermore, the data processing device can be set up to determine a measure of the measurement accuracy of the value indicative of the permittivity of the cell population on the basis of said spectral power and the total power, wherein the measure in particular the signal-to-noise ratio on the basis of said spectral power and the total power is.

According to a further embodiment, the conductors between the first scanning circuit and the first and / or second excitation electrode and the conductors between the second sensing circuit and the first and the second measuring electrodes are substantially equal in length. The term essentially the same length means that the conductors between the second scanning circuit and the first and the second measuring electrodes have between 90% and 110% of the length of the conductors between the first scanning circuit and the first and / or second exciter electrode, in particular between 95%. and 105%.

According to a further embodiment, the cell population sensor further comprises a control unit, which is coupled to the oscillator circuit and causes the oscillator circuit in operation to generate successively oscillating excitation currents through the cell population with different exciter frequencies. Furthermore, the control unit may be coupled to the first sampling circuit and the second sampling circuit and configured to transmit the currently generated excitation frequency to the first and the second sampling circuit. The first and second sampling circuits can accordingly set the sampling rate. The control unit can also be set up to transmit the currently generated excitation frequency to the data processing device.

Exemplary embodiments of the invention further comprise a computer program or a computer program product which contains program instructions which, when executed on a data processing system, perform a method according to one of the embodiments described above. The individual steps of the method can be initiated by the program instructions and executed by other components or executed in the data processing system itself.

• 1 zeigt einen Zellpopulationssensor gemäß einer beispielhaften Ausführungsform der Erfindung in einer Seitenansicht;
• 2 zeigt einen Zellpopulationssensor gemäß einer beispielhaften Ausführungsform der Erfindung, teilweise dargestellt als Blockschaltbild und teilweise dargestellt als Schaltungsdiagramm;
• 3 zeigt ein Ablaufdiagramm für ein Verfahren zum Herleiten von mindestens einer charakteristischen Eigenschaft einer Zellpopulation gemäß einer beispielhaften Ausführungsform der Erfindung; und
• 4 zeigt einen beispielhaften Verlauf von Permittivitätswerten gegenüber der Erregerfrequenz und illustriert das Herleiten von charakteristischen Eigenschaften der Zellpopulation.

Further exemplary embodiments of the invention will be described below with reference to the accompanying figures.

• 1 shows a cell population sensor according to an exemplary embodiment of the invention in a side view;
• 2 shows a cell population sensor according to an exemplary embodiment of the invention, partially shown as a block diagram and partially shown as a circuit diagram;
• 3 FIG. 10 is a flowchart for a method for deriving at least one characteristic of a cell population according to an exemplary embodiment of the invention; FIG. and
• 4 shows an exemplary course of permittivity values against the excitation frequency and illustrates the derivation of characteristic properties of the cell population.

1 shows a cell population sensor 2 according to an exemplary embodiment of the invention in a side view. The cell population sensor 2 is designed to determine a value indicative of the permittivity of a cell population, as described below. The cell population sensor 2 is designed for immersion in the cell population to be analyzed. For this purpose, the cell population sensor has 2 a rod-shaped sensor body 4 who in 1 is shown cut off. The rod-shaped sensor body 4 may be of suitable length such that analysis of the cell population may take place at a desired location in a vessel containing the cell population. At the end of the sensor body 4 is a sensor head 6 appropriate.

The sensor head 6 has four electrodes. In particular, the sensor head has 6 a first exciter electrode 8th , a second excitation electrode 10 , a first measuring electrode 12 and a second measuring electrode 14 , In the exemplary embodiment of 1 are the four electrodes 8th . 10 . 12 . 14 elongated. They run essentially parallel to the extension direction of the sensor body 4 , It is emphasized that the four electrodes may also be in other geometric configurations, eg in the form of rings or ring sectors around the sensor head.

In the exemplary embodiment of 1 are both the sensor body 4 as well as the electrode carrying part of the sensor head 6 cylindrically shaped. sensor body 4 and sensor head 6 But they can also have a different basic geometric structure.

In the exemplary embodiment of 1 are the first excitation electrode 8th and the second excitation electrode 10 at diametrically opposite locations of the sensor head 6 arranged. The first measuring electrode 12 and the second measuring electrode 14 are on one side of the sensor head 6 , in the view of 1 on the side facing the viewer of the sensor head 6 , between the first excitation electrode 8th and the second excitation electrode 10 arranged.

Here is the first measuring electrode 12 closer to the first exciter electrode 8th arranged and the second measuring electrode 14 closer to the second excitation electrode 10 arranged. Furthermore, the first and second measuring electrodes 12 . 14 the first and second excitation electrodes 8th . 10 arranged comparatively close. In particular, the first and second measuring electrodes 12 . 14 the first and second excitation electrodes 8th . 10 closer than an imaginary center line between the first excitation electrode 8th and the second excitation electrode 10 , By the arrangement of the measuring electrodes 12 . 14 between the exciter electrodes 8th . 10 and near the excitation electrodes 8th . 10 For example, a comparatively high voltage can be measured when the exciter current is applied.

2 shows a cell population sensor 2 according to an exemplary embodiment of the invention, partially in a block diagram and partially in a circuit diagram. The components of the cell population sensor 2 the 2 can in a cell population sensor of the 1 be present physical form shown. That is, in the circuitry and signal processing technology structure of the cell population sensor 2 the 2 It may be the structure of the electrical components of the cell population sensor 2 the 1 act. In doing so, the components that are in 2 are shown to the right of the circular drawn coupling points in the sensor body 4 or be housed in a subsequent component.

The cell population sensor 2 has the first excitation electrode described above 8th , second excitation electrode 10 , first measuring electrode 12 and second measuring electrode 14 , The four electrodes 8th . 10 . 12 . 14 are accessible from the outside, ie they are in contact with the cell population when the cell population sensor 2 immersed in the cell population for analysis of the cell population. Furthermore, a temperature sensor 58 provided outside the housing of the cell population sensor 2 lies.

The cell population sensor 2 has an oscillator circuit 16 , a signal detection and conditioning circuit 25 , a data store 36 , a data processing device 40 , a control unit 56 and a power management unit 38 on. The individual components and the mode of operation of these subsystems will be described in detail below.

The oscillator circuit 16 has an oscillator 18 on that with an oscillation amplifier 20 coupled, which in turn with a transformer 22 is coupled. The oscillator 18 is via a control input with the desired excitation frequency EF provided. The excitation frequency EF is from the control unit 56 as described in detail below, and to the oscillator 18 to hand over. The oscillator 18 generates a vibration with the exciter frequency EF which are connected to the oscillation amplifier 20 is handed over. The oscillation amplifier 20 generates a field current with the excitation frequency EF through the primary winding of the transformer 22 , By induction, the excitation current is applied to the secondary winding of the transformer 22 from where the power to the first and the second excitation electrode 8th . 10 is created. In this case, that is one end of the secondary winding via a first resistor 24 with the first excitation electrode 8th connected and the second end of the secondary winding via a second resistor 26 with the second excitation electrode 10 connected. Thus, a closed circuit results from the first end of the secondary winding through the first resistor 24 , via the first exciter electrode 8th through the cell population to the second excitation electrode 10 , and by the second resistance 26 to the second end of the secondary winding. In this way, one with the exciter frequency EF oscillating excitation current through the cell population between the first excitation electrode and the second excitation electrode 10 generated. In the exemplary embodiment of the 2 the excitation current is a sinusoidal, with the exciter frequency EF oscillating excitation current. Furthermore, the exciting current in the exemplary embodiment of the 2 an amplitude of 1 Vpp to 2 Vpp.

The transformer 22 provides a galvanic decoupling between the oscillation amplifier 20 and the first and second excitation electrodes 8th . 10 , It can have a coupling capacity in parallel with the transformer 22 be provided. You can also talk about that transformer 22 has a parallel capacitance existing between the primary winding and the secondary winding. The parallel capacitance may be a discrete component or a parasitic capacitance of the transformer. The parallel capacitance, by placing it in parallel with the transformer, can counteract interfering influences from other coupling capacities, such as coupling capacitances between the electrodes and the cell population receptacle and / or coupling capacitances between the electrodes and other sensors present in the cell population. The parallel capacitance can be between 1 pF and 5 pF.

By the oscillating with the excitation frequency EF excitation current between the first excitation electrode 8th and the second excitation electrode 10 creates an AC voltage between the first measuring electrode 12 and the second measuring electrode 14 , Both the excitation current and the voltage between the measuring electrodes 12 . 14 be through the signal detection and conditioning circuit 25 recorded and sampled. At the end of signal processing in the signal acquisition and conditioning circuit 25 are digital signals for the excitation current and the voltage between the measuring electrodes 12 . 14 ,

A first signal, which maps the exciting current, is obtained in the following way. The second resistance 26 acts as a measuring resistor for the excitation current. The voltage across the measuring resistor 26 is tapped by means of two conductors and as the first signal of a first amplifier circuit 28 fed. The amplified first signal becomes the first analog-to-digital converter 32 fed. There, the amplified first signal is converted into a digital signal, ie the amplified first signal is sampled and quantized. The resulting first samples are applied to the data memory 36 output. It can be seen that the first resistance 24 not required for obtaining the first signal. For symmetry reasons, the first resistance 24 but still provided. Furthermore, it can be seen that the picking up of an exciting current imaging signal also at the first resistor 24 can take place. That is, the first amplifier circuit could also be connected to the first excitation electrode 8th or the first resistor 24 be coupled. The first resistance 24 and the second resistance 26 can each have a value of 30 Ω to 50 Ω.

The voltage between the first measuring electrode 12 and the second measuring electrode 14 forms a second signal, which a second amplifier circuit 30 is supplied. There, the second signal is amplified, and the amplified second signal is a second analog-to-digital converter 34 fed. The second analog-to-digital converter generates, analogous to the first analog-to-digital converter 32 , second samples, which are time-discrete and quantized. The second samples are also sent to the data store 36 output.

The first analog-to-digital converter 32 and the second analog-to-digital converter 34 also receive the information about the exciter frequency EF from the control unit 56 , The first analog-to-digital converter 32 and the second analog-to-digital converter 34 use 4 times the excitation frequency EF for sampling the amplified first signal and the amplified second signal. Thus, create the first analog-to-digital converter 32 and the second analog-to-digital converter 34 first and second samples of the excitation current and the voltage between the measuring electrodes 12 . 14 with 4 times the excitation frequency EF.

That of the first analog-to-digital converter 32 and the second analog-to-digital converter 34 output first and second samples are in the data memory 36 cached. The data store 36 thus represents a depot that receives the first samples and the second samples and provides independent of real time for further data processing. Thus, there are from the data store 36 no real-time requirements for the downstream components anymore. On the contrary, the downstream components can be stored in the data store over a period of time 36 access. The data store 36 For example, it may be a DPRAM or any other suitable type of data store.

The data store 36 is with the data processing device 40 coupled and outputs the first samples for the excitation current and the second samples for the voltage between the first measuring electrode 12 and the second measuring electrode 14 to the data processing device 40 out. In the data processing device 40 There are two data processing paths, which are described below.

First, the first and second samples are applied to a Fourier transform module 42 to hand over. The Fourier transform module 42 performs a discrete, complex Fourier transform with the first samples for the excitation current and the second samples for the voltage between the measurement electrodes 12 . 14 by. The in the Fourier transform module 42 Fourier transformation performed is discrete and complex because the discrete-time samples of excitation current and voltage between the measuring electrodes are analyzed as interdependent quantities. The result of this complex Fourier transformation are the amplitudes of excitation current and measured voltage for different frequencies as well as the phase shift α between excitation current and measured voltage for the different frequencies. It is possible that the Fourier transform performs a wide spectral analysis of the samples and then all spectral components except the spectral components at the excitation frequency EF be discarded. But it is also possible that the Fourier transform targeted the spectral component of the excitation current and the spectral component of the voltage between the first measuring electrode 12 and the second measuring electrode 14 determined at the excitation frequency. In this context, also the Goertzel algorithm are used, with the targeted the spectral components at the excitation frequency EF can be determined.

The amplitude of the spectral component of the excitation current at the excitation frequency EF and the amplitude of the spectral component of the measured voltage at the excitation frequency EF are transmitted via a first data transmission connection 44 to the permittivity determination module 48 to hand over. The phase shift α between the spectral component of the excitation current at the excitation frequency and the spectral component of the measured voltage at the excitation frequency is via a second data transmission connection 46 to the permittivity determination module 48 to hand over.

The Permittivity Determination Module 48 determines a conductance from the transferred parameters G , a capacity value C , the conductivity σ of the cell population at the excitation frequency and the permittivity ε of the cell population at the excitation frequency. The conductance G and the capacitance value C can be calculated using the following two equations: G = cos (α) * (i / u); C = (tan (α) * G) / (2 * π * f), where i and u denote the amplitude of excitation current and measured voltage of the spectral component at the excitation frequency. From these formulas it can be seen that the capacitance value can also be calculated without detouring over the conductance value from α, i and u. But it is also possible that the conductance G and the capacity value C deriving from more complex models or calibrating the values calculated using the equations mentioned above.

The conductivity σ and the permittivity ε are subsequently derived from the conductance G and the capacity value C calculated using a model that maps the geometry of the cell population sensor and, where appropriate, other influencing the measurement results factors of the measuring arrangement. In this way, from the conductance G and the capacity value C the material properties conductivity σ and permittivity ε derived from the cell population. For the derivation of conductivity σ and permittivity ε For example, known approaches and methods can be used. By obtaining samples of exciter current and voltage between the measuring electrodes with high accuracy, ie by the high quality of the output data as described herein, even when using known methods for deriving conductivity σ and permittivity ε improved results can be achieved compared to previous cell population sensors.

On the other hand, the first and second samples are sent to an RMS calculation module 50 to hand over. The RMS Calculation Module 50 Determines the RMS values of the exciter current and the voltage between the measuring electrodes by means of root mean square 12 . 14 , The rms values of the excitation current and the voltage are transmitted via the third data transmission connection 52 to the SNR calculation module 54 to hand over. The abbreviation SNR stands for signal-to-noise ratio ("Signal to Noise Ratio"). The SNR calculation module 54 further receives the amplitude of the spectral component of the excitation current at the exciter frequency EF and the amplitude of the spectral component of the measured voltage at the excitation frequency EF over the first data connection 44 ,

The SNR calculation module 54 determines from the transferred data the spectral power of the excitation current and the voltage between the measuring electrodes 12 . 14 at the excitation frequency as well as the total power of the excitation current and the voltage between the measuring electrodes 12 . 14 , Based on these two performance parameters, the signal-to-noise ratio is determined. The signal-to-noise ratio can be determined, in particular, as the ratio of the stated spectral power to the total power minus the stated spectral power. The signal-to-noise ratio can be used as a measure of the accuracy of the determination of the capacitance value C or the permittivity ε are considered. In particular, the signal-to-noise ratio can be regarded as a measure of what proportion of the measured voltage of the response of the cell population can be attributed to the excitation current, which is indeed observed. It is emphasized that said spectral power at the exciter frequency and the total power may also be related in other appropriate ways to make a statement about the measurement accuracy. The signal-to-noise ratio is an exemplary measure.

Thus, the guide value G , the capacity value C , the conductivity σ, the permittivity ε and the signal-to-noise ratio as results of the signal processing in the data processing device 40 to disposal. In particular, these values are available as results for the excitation of the cell population at a particular excitation frequency. One or more of these values can be output for further processing. The output may be to an external unit or, as in the exemplary embodiment of FIG 2 shown to the existing in the cell population sensor control unit 56 respectively.

In the exemplary embodiment of the 2 are the value determined for the permittivity ε and the signal-to-noise ratio to the control unit 56 output.

The data processing device 40 may be implemented in software or as an array of hardware components. It is also possible that the data processing device 40 partly implemented in software and partly in hardware. The same applies to the control unit described below 56 ,

The control unit 56 is with the power management unit 38 , with the oscillator circuit 16 , with the signal detection and conditioning circuit 25 and with the data processing device 40 connected. The control unit 56 controls the method for determining a value indicative of the permittivity of a cell population according to exemplary embodiments of the invention. This is the control unit 56 set up to set the excitation frequency EF for the procedure. In particular, the control unit is set up to set a plurality of exciter frequencies for a plurality of passes of the method in the context of an impedance spectroscopy.

For a given pass, the control unit transmits 56 the fixed exciter frequency EF to the oscillator circuit 16 where the oscillator 18 a vibration with the excitation frequency EF generated to the signal acquisition and conditioning circuit 25 where the first analog-to-digital converter 32 and the second analog-to-digital converter 34 set the sampling rate based on the excitation frequency EF, and to the data processing device 40 where the Fourier transform module 42 the samples of excitation current and voltage between the measuring electrodes 12 . 14 analyzed with respect to the spectral signal components at the excitation frequency.

Furthermore, the control unit 56 in the exemplary embodiment of 2 with the data processing device 40 coupled in that the data processing device 40 the permittivity ε determined for the exciter frequency EF and the signal-to-noise ratio determined in the determination of the permittivity to the control unit 56 transmitted. The control unit 56 is arranged to decide on the basis of the determined signal-to-noise ratio whether a further run of the method is undertaken in order to determine the permittivity for the given excitation frequency EF with a better signal-to-noise ratio, or if the result is considered to be of high quality is accepted. In the second case, the control unit 56 define an excitation frequency for the next run of the method in the context of impedance spectroscopy. It is also possible that the control unit 56 for each of the desired excitation frequencies only one pass of the method is made, no matter how good the signal-to-noise ratio, and outputs the signal-to-noise ratio merely as additional information.

After a plurality of permittivity values have been determined for different exciter frequencies, the control unit may 56 derive one or more characteristic properties of the cell population from the plurality of permittivity values. For this, the control unit may make a curve through the plurality of permittivity values and derive from the curve the characteristic properties of the cell population, as described below with reference to FIG 4 described. Such relationship of the plurality of permittivity values may also be outside the cell population sensor 2 respectively.

The control unit 56 is with the power management circuit 38 coupled to signal the beginning and the end of a run of the process. The power management circuit 38 supplies the oscillation amplifier on the basis of these signals 20 and the first amplifier circuit 28 and the second amplifier circuit 30 with the positive supply voltage V + and the negative supply voltage V-, which are +4.5 V and -4 V in the present exemplary embodiment. After the end of a run of the process disconnects the power management circuit 38 the positive and the negative supply voltage and transmitted to the oscillator 18 , the first analog-to-digital converter 32 , the second analog-to-digital converter 34 and the data store 36 a shutdown signal ("power down"). In this way, the cell population sensor saves electrical energy between runs of the method for determining permittivity.

The power management circuit 38 can electrical energy from outside the cell population sensor 2 or have an internal energy reservoir, eg in the form of a battery.

To protect the cell population sensor 2 can the power management circuit 38 open the power supply when the temperature sensor 58 measures a temperature above a predetermined threshold.

3 shows a method 100 for deriving at least one characteristic of a cell population according to an exemplary embodiment of the invention. The procedure 100 for example, from the in 1 and 2 shown cell population sensor 2 be performed. This is the cell population sensor 2 at least with his electrodes 8th . 10 . 12 . 14 immersed in the cell population to be analyzed.

The procedure 100 starts with the "Start" step 102 , In step 102 a frequency index n is set to 1. The frequency index indicates the instance of performing the method for determining a value indicating the permittivity of the cell population. In other words, the frequency index states how many excitation frequencies are used in the given run. Before starting the procedure, it is clear how many different excitation frequencies are used. For example, between 20 and 30 different excitation frequencies can be used. There may also be a table that includes an exciter frequency for each value of the frequency index. It is also possible that the excitation frequency is determined according to a predetermined rule for each value of the frequency index. For example, it is possible for the excitation frequencies to be selected in a regular manner from a logarithmic scale. For example, the following frequencies can be used as excitation frequencies: 50 kHz, 60 kHz, 70 kHz, 80 kHz, 90 kHz, 100 kHz, 200 kHz, 300 kHz, 400 kHz, 500 kHz, 600 kHz, 700 kHz, 800 kHz, 900 kHz, 1 MHz, 2 MHz, 3 MHz, 4 MHz, 5 MHz, 6 MHz, 7 MHz, 8 MHz, 9 MHz, 10 MHz, 20 MHz. However, any other suitable amount of excitation frequencies is also possible for carrying out the method.

In step 104 become the positive supply voltage V + and the negative supply voltage V-, also called analog supply, switched on. In step 106 become the oscillator 18 , the first analog-to-digital converter 32 , the second analog-to-digital converter 34 and the data store 36 activated. In step 108 the exciter frequency, also called the stimulus frequency, is set. For this purpose, the associated frequency is determined for the current value of the frequency index and set as the excitation frequency. The oscillator circuit 16 begins to apply the excitation current with the excitation frequency to the cell population. In step 110 is in the first analog-to-digital converter 32 and the second analog-to-digital converter 34 the sampling rate, also referred to as the sampling rate, set to 4 times the exciter frequency. In step 112 be in the first analog-to-digital converter 32 generates first samples, also referred to as first samples. Furthermore, in the second analog-to-digital converter 34 second samples, also referred to as second samples, generated. The first samples and the second samples are in step 112 in the data store 36 written. In step 114 become the oscillator 18 , the first analog-to-digital converter 32 , the second analog-to-digital converter 34 and the data store 36 disabled. In step 118 the analog supply is switched off, ie the positive supply voltage V + and the negative supply voltage V- are decoupled.

In step 118 On the one hand, the amplitude of the exciting current, ie the amplitude of the exciting current oscillating with the exciting frequency, the amplitude of that spectral component of the measured voltage having the exciting frequency, and the phase shift between the exciting current and said spectral component of the measured voltage determined. On the other hand, the rms values of the exciting current and the total voltage between the measuring electrodes become 12 . 14 certainly. In step 120 the signal-to-noise ratio SNR is determined on the basis of the spectral power at the excitation frequency and the total power and compared with a signal-to-noise ratio threshold value SNR '. When the determined signal-to-noise ratio SNR below the threshold value SNR ', in step 122 detected a fault.

In step 124 become the guiding value G and the capacity value C calculated as described above. In step 126 become the guiding value G and / or the capacity value C calibrated. It can also be said that the conductance G and / or the capacity value C be corrected using a calibration rule. The calibration data may be in a table and / or in a functional form. Based on the calibrated values for conductance G and capacity value C be in step 128 the conductivity σ and the permittivity ε are calculated.

In step 130 It is decided first whether due to an eventual step 122 detected disturbance of the pass should be repeated for the present excitation frequency. In this case, the frequency index is not increased, and the procedure 100 moves to step 132 continued. If no fault has been detected, in step 130 checks if all desired excitation frequencies have been used, ie if the frequency index has reached its final value. If not, the frequency index is incremented by 1, and the procedure 100 moves to step 132 continued. When the frequency index has reached its final value, the procedure continues 100 with step 134 continued.

step 132 just means a delay before the procedure 100 at step 104 is resumed. The delay can reduce the electrical effects introduced in the previous run in the cell population. The next run can begin from a well-defined state of the cell population.

In step 134 From the plurality of values for the permittivity of the cell population, which have been determined for the different exciter frequencies, one or more characteristics of the cell population are derived. In particular, one or more of the number of living cells, size of the cells and homogeneity of the cells derived as related below 4 will be described in detail. The derived characteristics may be output to a user of the cell population sensor, for example via a screen. In addition to the characteristics, a quality measure may also be output, which may be derived from the above-discussed SNR values for the individual runs for determining the permittivity values. In step 136 the procedure ends 100 ,

4 shows purely qualitatively the course 200 the permittivity ε of a cell population plotted against the excitation frequency f. The history 200 is a purely exemplary curve derived from a plurality of values for the permittivity determined by the method described above. For example, the history may be 200 be derived from the plurality of Permittivitätswerten by means of a Cole-Cole fitting.

From the course 200 In this way characteristics of the cell population can be derived as follows. In 4 is qualitatively shown to be one for the β dispersion area 202 characteristic frequency f _ch a plateau area 204 is located in which the permittivity ε, compared with the area around the characteristic frequency f _ch , with the frequency changes only slightly, and that according to the characteristic frequency f _ch another plateau area 206 which is situated on the plateau area 22 before the characteristic frequency f _ch is different and in which the permittivity ε, again compared to the area around the characteristic frequency f _ch , also does not change much with the frequency.

If one compares a permittivity value representing the permittivity ε ε ₁ at an excitation frequency f ₁ in the plateau area 204 with a permittivity value ε ₂ at an excitation frequency f ₂ in the plateau area 206 , so can be seen from the at the exciter frequencies f ₁ and f ₂ certain permittivity values ε ₁ or. ε ₂ determine a difference Δε of the two permittivity values. The difference Δε is a measure of the number of living cells contained in the cell population. The alternate permittivity curve indicated by two dots and three dashes 210 would result in a magnitude larger Δε at the respective exciter frequencies f ₁ and f ₂ which allows conclusions to be drawn that the cell population for which the permittivity curve 210 was obtained, has more living cells in the same volume than that of the Permittivitätskurve 200 underlying cell population.

A change in the characteristic frequency f _ch indicates a change in the size of the cells or their physiology. A permittivity curve 220 with two dots and a dash shows a higher characteristic frequency f _ch in 4 , The characteristic frequency f _ch may be from the turning point of the course 200 between the plateau area 204 and the plateau area 206 be determined.

The slope of the permittivity curve at the point of its characteristic frequency f _ch is a measure of cell size distribution, with increasing slope indicating a more heterogeneous cell size distribution, and flatter progressions of the permittivity curve 200 at the location of the characteristic frequency f _ch mean more homogeneous cell size distributions.

In the 4 In particular, the courses of the real parts of the determined permittivity values can be shown.

In the exemplary embodiment of the 4 f ₁ = 50 kHz and f ₂ = 20 MHz. Cell population sensors in accordance with exemplary embodiments of the invention allow for highly accurate determination of permittivity values over such a broad frequency range, thereby allowing the β-dispersion region to be described very extensively for many cell populations. In particular, the cell population sensor and the method for determining a permittivity of a cell population indicative value according to exemplary embodiments of the invention are suitable for cell populations with a conductivity of a few 0.1 mS / cm to 100mS / cm and a permittivity of a few pF / cm to several hundred pF /cm.

An exemplary use case for the cell population sensor and the method for determining a value indicative of the permittivity of a cell population according to exemplary embodiments of the invention are fermentation processes, for example, in brewing beverages. However, the invention is generally broadly applicable for determining values indicative of the permittivity of a cell population.

Although the invention has been described with reference to exemplary embodiments, it will be apparent to those skilled in the art that various changes may be made and equivalents may be employed without departing from the scope of the invention. The invention should not be limited by the specific embodiments described. Rather, it includes all embodiments that fall under the appended claims.

Claims (40)

Method for determining a value indicative of the permittivity of a cell population in the context of impedance spectroscopy, comprising the following steps: Generating an excitation current oscillating with an exciter frequency through the cell population, Measuring a voltage in the cell population between a first measuring electrode (12) and a second measuring electrode (14), Sampling the excitation current, wherein first samples of the excitation current are generated, Sensing the voltage between the first measuring electrode (12) and the second measuring electrode (14), thereby generating second samples of the voltage between the first measuring electrode and the second measuring electrode, and Determining the value indicative of the permittivity of the cell population based on the first samples and the second samples. Method according to Claim 1 wherein sampling the exciting current and sensing the voltage between the first sensing electrode (12) and the second sensing electrode (14) each include converting an analog signal to a digital signal. Method according to Claim 1 or 2 , further comprising the steps of: setting a first sampling rate for sampling the exciting current, and setting a second sampling rate for sampling the voltage between the first measuring electrode (12) and the second measuring electrode (14). Method according to Claim 3 , Wherein the first sampling rate and the second sampling rate are set to at least 4 times the excitation frequency of the excitation current, in particular substantially to 4 times the excitation frequency of the excitation current. Method according to one of the preceding claims, wherein the exciter frequency of the excitation current is between 50 kHz and 20 MHz. Method according to one of the preceding claims, wherein the scanning of the excitation current and the sampling of the voltage between the first measuring electrode (12) and the second measuring electrode (14) are synchronized. Method according to one of the preceding claims, further comprising the step: Writing the first samples and the second samples into a data memory (36), the data memory being capable in particular of receiving data at a data acquisition rate of at least 1 Gbit / s. The method of any one of the preceding claims, wherein the step of determining the value indicative of the permittivity of the cell population includes applying a complex Fourier transform to the first samples and the second samples. The method of any one of the preceding claims, wherein the step of determining the value indicative of the permittivity of the cell population comprises at least one of the following steps: Determining the amplitude of the oscillating excitation current, Determining the spectral component of the voltage having the excitation frequency, and Determining the phase shift between excitation current and said spectral component of the voltage. The method of any one of the preceding claims, wherein the step of determining the value indicative of the permittivity of the cell population further comprises the step of: Determining the value indicative of the permittivity of the cell population based on one or more of the amplitude of the oscillating excitation current, the amplitude of that spectral component of the voltage having the excitation frequency, and the phase shift between the excitation current and the said spectral component of the voltage. Method according to one of the preceding claims, wherein the value indicative of the permittivity of the cell population is a capacitance value or a permittivity value. Method according to one of the preceding claims, wherein the step of sampling the excitation current includes amplifying a first signal representative of the exciter current before the first samples are generated based on the amplified first signal, and / or wherein the step of sensing the voltage between the first sensing electrode (12) and the second sensing electrode (14) includes amplifying a second signal representative of the voltage between the first sensing electrode and the second sensing electrode before the second sensing values are generated based on the amplified second signal become. Method according to one of the preceding claims, further comprising the step: Generating a first signal representing the exciting current via a measuring element (26), in particular via a measuring resistor. Method according to one of the preceding claims, wherein generating the with the Excitation frequency oscillating excitation current through the cell population includes a galvanic decoupling between an excitation current emitting AC source and the cell population. Method according to one of the preceding claims, further comprising the following steps: Determining a spectral power of the excitation current and the spectral component of the voltage having the excitation frequency, Determining the total power of exciting current and voltage between the first measuring electrode (12) and the second measuring electrode (14), and Determining a measure of the measurement accuracy of the value indicative of the permittivity of the cell population on the basis of said spectral power and the total power, wherein the measure is in particular the signal-to-noise ratio based on said spectral power and the total power. Method for deriving at least one characteristic property of a cell population, comprising the following steps: repeatedly performing the method of determining a cell population permittivity value according to one of the preceding claims using a plurality of different excitation frequencies and determining a plurality of cell population permittivity indicative of the plurality of different excitation frequencies, and Deriving the at least one characteristic property of the cell population by relating the plurality of values indicative of the permittivity of the cell population. Method according to Claim 16 wherein said method for determining a value indicative of the permittivity of a cell population for between 2 and 50 different excitation frequencies, in particular for between 10 and 40 different exciter frequencies, more particularly for between 20 and 30 different exciter frequencies. Method according to Claim 16 or 17 , wherein the different excitation frequencies from a frequency range of 100 kHz to 10 MHz, in particular from a frequency range of 50 kHz to 20 MHz, come. Method according to one of Claims 16 to 18 wherein each instance of repeatedly performing the method for determining a value indicative of the permittivity of a cell population lasts between 10 ms and 100 ms, in particular between 30 ms and 70 ms. Method according to one of Claims 16 to 19 wherein deriving the at least one characteristic characteristic of the cell population includes establishing a history of the permittivity of the cell population indicative of values across the different excitation frequencies. Method according to one of Claims 16 to 20 in which the at least one characteristic characteristic of the cell population comprises at least one property of number of living cells, size of the cells and homogeneity of the cells. A cell population sensor (2) for determining a value indicative of the permittivity of a cell population, comprising: an oscillator circuit (16), a first exciter electrode (8) and a second exciter electrode (10), which are coupled to the oscillator circuit (16), wherein by means of the oscillator circuit (16) via the first and the second excitation electrode (8, 10) an exciting current oscillating with an exciter frequency the cell population can be generated, a first measuring electrode (12) and a second measuring electrode (14) for measuring a voltage in the cell population between the first and second measuring electrodes (12, 14), a first sampling circuit (32) coupled to the first excitation electrode (8) and / or the second excitation electrode (10) and providing in operation first samples of the oscillating excitation current, a second sense circuit (34) coupled to the first and second sense electrodes (12, 14) and in operation providing second samples of the voltage between the first and second sense electrodes, and data processing means (40) coupled to the first sampling circuit and the second sampling circuit and configured to determine the value indicative of the permittivity of the cell population based on the first samples and the second samples. Cell population sensor (2) after Claim 22 wherein the first sampling circuit (32) is a first analog-to-digital converter, and wherein the second sampling circuit (34) is a second analog-to-digital converter. Cell population sensor (2) after Claim 22 or 23 wherein the first sampling circuit (32) has a first settable sampling rate and wherein the second sampling circuit (34) has a second settable sampling rate. Cell population sensor (2) after Claim 24 wherein the first adjustable sampling rate and the second adjustable sampling rate are adjustable to at least 4 times the excitation frequency of the exciter current, in particular substantially to 4 times the excitation frequency of the exciter current. Cell population sensor (2) according to one of Claims 22 to 25 wherein the oscillator circuit (16) is arranged to set the excitation frequency in a frequency range of 100 kHz to 10 MHz, in particular in a frequency range of 50 kHz to 20 MHz. Cell population sensor (2) according to one of Claims 22 to 26 wherein the first sampling circuit (32) and the second sampling circuit (34) are synchronized with respect to their sampling timings. Cell population sensor (2) according to one of Claims 22 to 27 in that the first scanning circuit (32) and the second scanning circuit (34) are coupled to the data processing device (40) via a data memory (36), the data memory (36) in particular having a data acquisition rate of at least 1 Gbit / s. Cell population sensor (2) according to one of Claims 22 to 28 wherein the data processing device (40) is arranged to determine the value indicative of the permittivity of the cell population by means of complex Fourier transformation from the first samples and the second samples. Cell population sensor (2) according to one of Claims 22 to 29 wherein the data processing means (40) is arranged to determine at least one of amplitude of the oscillating exciting current, amplitude of that spectral component of the voltage having the exciting frequency, and phase shift between exciting current and said spectral component of the voltage from the first samples and the second samples. Cell population sensor (2) according to one of Claims 22 to 30 wherein the data processing means is arranged to determine the permittivity of the population of cells based on one or more of the amplitude of the oscillating exciting current, the amplitude of that spectral component of the voltage having the exciting frequency, and the phase shift between exciting current and said spectral component of the To determine tension. Cell population sensor (2) according to one of Claims 22 to 31 wherein the value indicative of the permittivity of the cell population is a capacitance value or a permittivity value. Cell population sensor (2) according to one of Claims 22 to 32 wherein the first sampling circuit (32) is coupled to the first excitation electrode (8) and / or the second excitation electrode (10) via a first amplifier circuit (28), and wherein the second sampling circuit (34) is connected to the first sampling circuit (30) first and the second measuring electrode (12, 14) is coupled. Cell population sensor (2) according to one of Claims 22 to 33 in which a measuring element (26), in particular a measuring resistor, is coupled to the first exciter electrode or the second exciter electrode, and wherein the first scanning circuit (32) is arranged to generate the first samples for the oscillating exciter current on the basis of the voltage drop across the measuring element (26). provide. Cell population sensor (2) according to one of Claims 22 to 34 wherein the oscillator circuit (16) is coupled to the first exciter electrode (8) and the second exciter electrode (10) via a transformer (22). Cell population sensor (2) after Claim 35 wherein the transformer (22) has a parallel capacitance of 0.5 to 10 pF, in particular 1 to 5 pF. Cell population sensor (2) according to one of Claims 22 to 36 wherein the data processing means (40) is arranged to determine a spectral power of the exciting current and the spectral component of the voltage having the exciting frequency and to determine the total power of exciting current and voltage between the first measuring electrode and the second measuring electrode, and wherein the data processing means Furthermore, it is arranged to determine a measure of the measurement accuracy of the value indicative of the permittivity of the cell population on the basis of said spectral power and the total power, wherein the measure is in particular the signal-to-noise ratio on the basis of said spectral power and the total power. Cell population sensor (2) according to one of Claims 22 to 37 wherein the conductors between the first sensing circuit (32) and the first and / or second excitation electrodes (8, 10) and the conductors between the second sensing circuit (34) and the first and second sensing electrodes (12, 14) are substantially equal in length are. Cell population sensor (2) according to one of Claims 22 to 38 , further comprising a control unit (56) coupled to the oscillator circuit (16) and, in operation, causing the oscillator circuit to generate oscillating excitation currents through the cell population successively at different excitation frequencies. Computer program containing program instructions which, when executed on one Data processing system a method according to one of Claims 1 to 21 carry out.

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